French diplomat Joseph Comte de Gobineau published Religions et les Philosophies dans l'Asie Centrale, over half of which is devoted to a study of the Bábí movement.

Gobineau's work was written when Mírzá Yahyá was still know as the nominal head of the Bábí Faith between 1855 and 1858 when Gobineau was First Secretary and Chargé d'Affaires of the French Legation. Two embassy employees during his time there were ardent supporters of Mírzá Yahyá, one of whom was his brother-in-law. (He served as the Ambassador from March 1862 until September, 1863.)

This work attracted a number of other European intellectuals, including E. G. Browne of Cambridge, who eventually became the most prolific western writer and researcher of the Bábi religion. [BBR17, MCS483; 500; 512]

A.L.M. Nicolas published his book Seyyed Ali dit le Bab. It was the first work by a western author dedicated entirely to the Báb.
It is "(a) history of the Bábí movement up to 1852. Nicolas gives a list of sources for this book on pp. 48-53. It is interesting to note that among his oral sources are four of the leading Bahá'ís of that period, who had been designated by Bahá'u'lláh as 'Hands of the Cause': Mírzá 'Alí-Muhammad, 'Ibn-i-Asdaq: Mullá 'Al-Akbar-i-Sháhmírzádí, Hají Akhund; Mírzá Muhammad-Táqíy-i-Abharí, 'Ibn-i-Abhar; and Mírzá Hasan-i-Adíb.
The other two oral sources named are Siyyid 'Ismu'lláh, who was presumably Siyyid Mihdíy-i-Dihají, and Mírzá Yahyá, Subh-i-Azál."
[BBR38-39]

The preamble to his book has an image that is supposedly of the Báb, but the portrait does not seem to be an authentic representation.

William Miller also reproduced Nicolas’s image on page 17 of his polemical work, The Bahá'í Faith: Its History and Teachings. (South Pasadena, CA: William Carey Library, 1974). [‘The Bab in the World of Images’, Baha’i Studies Review, vol. 19, June 2013, 171–90.]

Primary Source Texts, Access to, by Universal House of Justice and Susan Maneck (1998). One scholar's query why the Baha'i World Centre's copies of primary sources in Babi and Baha'i history are not available for study, followed by the House's response. [about]

Social Basis of the Bábí Upheavals in Iran (1848-1953): A Preliminary Analysis, by Moojan Momen, in International Journal of Middle East Studies, 15 (1983). In the mid-19th century, Iran was shaken by unrest caused by the Babi movement, which set off a chain of events that led on the one hand, to the constitutional movement in Iran, and on the other, to the establishment of the now world-wide Baha'i Faith. [about]